1. Field of the Invention
The present invention relates to compound paper making fabrics, especially to forming fabrics, for use in a paper machine to manufacture a fibrous web.
2. Discussion of Background Information
Various styles of paper making fabrics, especially forming fabrics are known in the art.
EP 1 294 981 discloses a compound forming fabric for use in the forming section of a paper making machine comprising a paper side fabric and a wear side fabric being bound together by pairs of binding threads forming part of the weave pattern of the paper side fabric and part of the weave pattern of the wear side fabric and alternate from weaving with the paper side fabric to weave with the wear side fabric and vice versa, thereby crossing each other by forming crossing points. The forming fabric according to EP 1 294 981 shows per wear side weave repeat two crossing points. The structure has a high number of crossing points each of which destroys the planarity of the paper contacting side of the paper side fabric resulting in markings of the paper sheet.
In this manner, a warp exchange forming fabric is formed using two warp yarns that make a single knuckle with the wearside weft. The combination paths of these two exchanging warp yarns make up the wear side weave. However, the disadvantages include that the warp is weaving with the paperside for a limited length, thereby creating numerous exchange points per square meter. Each of these warp exchanges that results in a knuckle has the potential to form an indentation, or crater, resulting in uneven paper side fabric surface, which in turn has the high potential to “mark” the paper web and resultant paper sheet.
In EP 0 432 413, a compound forming fabric for use in the forming section of a paper making machine is disclosed whereby a paper side fabric and a wear side fabric are bound together by pairs of binding threads forming part of the weave pattern of the paper side fabric and part of the weave pattern of the wear side fabric and alternate from weaving with the paper side fabric to weave with the wear side fabric and vice versa. According to EP 0 432 413, the number of paper side weft yarns is similar to the number of wear side weft yarns, resulting in a structure having a relative coarse paper contacting surface because of the relative low number of paper side weft yarns per length unit, thereby leading to marking of the paper sheet formed on the fabric.